The mechanism of irreversible cellular damage during myocardial ischemia will be investigated in isolated perfused rat hearts. Preliminary data indicate that high levels of intracellular products of glycogenolysis accelerate the transition from reversible to irreversible damage independent of changes in tissue high energy phosphates. The hypothesis to be tested is that accumulation of glycolytic products (lactate, NADH, H+, etc.) in response to decreased coronary flow and oxidative metabolism initiates a series of secondary reactions that ultimately cause irreversible damage to the tissue. The proposed work will determine the temporal relation between tissue levels of glycolytic products during ischemia and the loss of contractile function in ischemic hearts subsequently reperfused under aerobic conditions. Accumulation of glycolytic products during ischemia will be varied by prior glycogen depletion, maintenance of different rates of ischemic coronary flow with anoxic perfusate and use of glycolytic inhibitors. Studies are proposed to allow identification of the responsible product(s). The temporal relationship between onset of irreversible damage and the appearance of alterations in mitochondrial, sarcolemmal and sarcoplasmic reticular functions will be determined in ischemic tissue exposed to a wide range of intercellular concentrations of glycolytic products to help characterize the mechanisms of glycolytic product induced cellular damage. The concentration of these products will be varied together and individually. Inhibitors of glycolysis will be developed in an attempt to provide prolonged protection to ischemic myocardium.